Thursday, November 7, 2013

Spending a warm summer night under the stars can
be one of the most enjoyable, relaxing experiences around for anyone,
serious astronomer or not. Unfortunately, the weather is not always
conducive to comfortable astronomy, often the exact opposite in the
case. As any astronomer who has gone through a full year of observing
can say, there's nothing colder than a clear winter night. Herein
arises the question: how to keep warm?

The bad part about
astronomy is that it is a stationary hobby so, without any movement
to build up body heat, you can get cold really quick. As a general
rule, seasoned astronomers will always tell a newcomer to dress (or
at least have handy) clothing that will suffice if it were actually
10 degrees colder than the forecast low for the night. Bottom line,
if it's going to get down to 50 tonight, dress as though it were
going to be 40. Another tip: layer up. When layering, your body heat
will warm up the air between the layers of clothing, providing for
some very effective insulation. As hard as it may be to believe,
layering three lightweight coats can actually be as warm as (or
warmer) than a single winter coat. Try it and see.

Statistically, most people in the developed
world live in cities/suburbs, which are not all that great settings
for doing astronomy. In fact, living in such a location probably
prevents a great number of people from taking up astronomy in the
first place, which need not happen as there are ways to beat the
light. First of all, what does light pollution look like?

Have
you ever gone outside on a cloudy night and noticed how light it was?
The answer to this question, for anyone living in a city/suburb is
going to be “a lot.” This effect can be greatly magnified when
there is a snowstorm overnight, too. Naturally, none of this light is
natural. In its purest form, a cloudy night should be dark, not have
a reddish hue to it. Needless to say, this is a very practical
example of light pollution, or stray light beamed away from the
ground that serves no other purpose than to brighten up the
sky.Now, this is not to say all light pollution is this bad, as
there can be greatly varying levels that can present themselves in
different ways.

In
2001, John Bortle devised a scale for determining light pollution.
The scale runs from one to nine, with higher numbers indicating more
light pollution. Here is a breakdown of the scale, magnitudes listed
are for people with exceptionally good vision.

Level
1: Excellent dark sky site, stars as dim as magnitude +8. The
brightest areas of the Milky Way cast very visible shadows. Bright
planets, Venus, Jupiter, Mars at a close approach, all seem to
inhibit proper night vision. This is an observers dream.

Level
2: Typical dark sky sight, stars to magnitude +7.5. The Summer Milky
Way is structured to the naked eye, the Zodiacal Light is still
bright enough to cast shadows. Many globular clusters are naked eye
objects.

Level
3: Rural sky, stars to magnitude +7. Only a hint of light pollution
near the horizon, where clouds may appear slightly illuminated.
Clouds dark overhead, appear as a starless black void in the sky.
Zodiacal Light rises over 60 degrees when standing straight up. Any
telescopes are apparent only to about 30 feet.

Level
4: Rural/suburban transition, stars to magnitude +6.5. Light
pollution domes over cities are apparent, clouds are illuminated in
brighter areas of sky, but still dark overhead. Zodiacal Light
extends about 45 degrees up at best. Milky Way still easily visible,
but most detail is now gone.

Level
5: Suburban, magnitudes to +5.9. Only hints of Zodiacal Light visible
on best nights. Milky Way only a faint haze near zenith and washed
out near horizon. Light sources very apparent, any clouds are
brighter than the sky.

Level
6: Bright suburban sky, magnitudes to +5.5. Zodiacal Light now
invisible and only a hint of the Milky Way is seen near the zenith.
Clouds are fairly bright. You will have no trouble seeing eyepieces
on a table at a distance. The third of sky nearest to horizon glows a
grayish-white color.

Level
7: Suburban/urban transition, magnitudes to +5. Entire sky has a
grayish-white hue to it. Milky Way now invisible, clouds appear as
glowing.

Level
8: City sky, to magnitude +4.5 at best. Sky begins to take on an
orange glow, you can read newspaper headlines easily. Constellations
incomplete as dim stars are now invisible.

Level
9: Inner city sky, magnitudes of +4 or less. Sky is lit to zenith,
All but the brightest constellations appear incomplete, dim
constellations are invisible.Not
only where you observe from can impact what you see, but the
characteristics of the air itself can play a huge role. Humid air is
an observer’s second worst enemy, only behind light pollution. For
visual observers, all of the tiny water droplets in the air reflect
light, thus magnifying any already existing light pollution. The
drier the air, the better the observing. On the most humid of Summer
nights in suburbia, third magnitude stars can be a challenge.
However, a few days later on a dry night, the Milky Way might be
visible from Zenith down to about 45 degrees. This vast difference in
what is visible can be due to humidity alone.

Now, light
pollution understood, how to beat it?

The easiest way (other than driving
out into the country) is to simply go to the backyard. Think about
it: do people put lights behind their houses? Without all of the walk
lights on the fronts of houses, the backyard is a lot darker than the
front. In addition, houses are great blockers from street lights,
too. So, without all of this artificial lighting, it's an easy claim
that you can drop one level of John Bortle's scale just by changing
your observation location without leaving one's own property.

For
someone really dedicated and who has a little money to burn, it might
be a good idea to build a small, privacy fence-enclosed area in one'
s backyard. By doing this, one can block out even more light. By
doing so, one can block out all the stray light coming in from the
sides, preserving night vision by allowing only a straight up view of
the night sky. To add to a fenced in area's effectiveness, paint the
inside of the walls flat black so prevent any reflectivity.

If
you are really serious about your astronomy and have a lot of money
to spend, it may be a good idea to invest in a small observatory. As
funny as it may seem to a beginner, many companies sell
ready-to-build observatory kits. By building an observatory, one can
block out even more light than with a privacy fence and, in addition,
have an outdoor storage space for all of one's astro toys.

Humans
are not designed to be nocturnal; therefore the human eye is not as
well suited to nighttime viewing as a night animal, say a cat’s.
The reason for this inability to see as well at night as a cat is
that the pupil of the human eye does not open nearly as wide as a
cat's. The pupil is what controls the amount of light allowed into
the eye. Naturally, for seeing in the dark, the ability to let in as
much light possible is important. If you look at a cat in a
relatively dark setting, you will see that the iris, the colored
part, of the cat’s eye is almost completely blocked out by the
black pupil. This is because the pupil is almost completely open,
which lets in the most light possible, which translates to excellent
night vision. In bright sunlight, a cat's pupil appears as a tiny
black slit in the middle of the colored iris. Unfortunately, for
naked eye astronomers, the human pupil can not open up to the amount
that a cat’s can. The good news is that the human pupil can open up
to a certain degree, the bad news is that this process takes about
ten to fifteen minutes. So, before stargazing, give your eyes at
least ten minutes to adjust to the dark. Once you get used to looking
at the stars, you will notice a difference. Many more stars will be
visible after ten minutes than after just after stepping out of your
probably well-lit house, human night vision at work.

Once
optimum night vision has been achieved over the course of about ten
minutes, a split second can ruin it. Since the human eye is more
adept at picking up light than seeing in the dark, the pupil quickly
dilates, or closes at the sight of a bright light. Once dilated by a
bright light, it will take time to re-achieve night vision, with time
being directly dependent on the intensity and color of the light,
which is also an important consideration.

The spectrum of
visible light runs from red, orange, yellow, greed, blue, indigo, and
violet (thing 'Roy G. Biv'). Colors on the red end of the spectrum
have longer wavelengths and less powerful frequencies than the short
wavelength light on the violet end of the spectrum. Since the power
of the wavelength can vary with color, it should come as no surprise
that reddish colors with longer wavelengths at lower frequencies are
less damaging to night vision than other colors. This lesson on the
color spectrum explains why you will only see red shaded flashlights
at any gathering of observational astronomers.

Getting back to
night vision, it is a good idea to go behind your house if you live
in a suburban setting to avoid all of the car headlights going up and
down the street, with each pass re-ruining your night vision. In
addition to escaping from headlights, escaping street and house
lights can do wonders for the amount of stars you will be able to
see.

While
many people are all about the telescope, the eyepiece often comes as
an afterthought. For a serious astronomer, this can be somewhat of a
mystery as the eyepiece can go a long way in making viewing more
enjoyable or, at the least, more varied.

The first question many
people have with eyepieces is 'how powerful is it?' Well, there is no
single answer to that question as eyepiece power is directly related
to what telescope it is being used with. To find eyepiece power,
simply divide the telescope's focal length by the eyepiece's focal
length. Example: a 10mm eyepiece in 1000mm scope (1000 divided by 10)
results in 100x power. In a 500mm scope, that same 10mm eyepiece
results in 50x power (500 divided by 10).

Another thing to
consider about eyepieces is the size of the opening through which you
look. Old-fashioned eyepieces resemble peepholes when of short
(powerful) focal lengths. Now, thanks to computer design and
ever-increasing creativity, some short focal length eyepieces can
have massive openings, providing bay window-like views to the
universe.

A final consideration of eyepieces is their angular
field of view. Needless to say, the wider the field, the better.
Unfortunately, for those super-wide, 90+ degree fields, you'll be
paying a lot of money and using eyepieces that seem to weigh as much
as bricks.

Lastly, good eyepieces come in two sizes: 1.25 and 2
inch diameters. The small, .965 eyepieces bundled with some
department store telescopes are a sure sign of a junk telescope as no
modern company with any degree of self-respect would market such a
product.

For
many beginning astronomers, the mount the telescope sits on is often,
erroneously, an afterthought. Bottom line: the mount can make or
break the observing experience whether it be through merely being too
small or simply not having the desired functionality. Telescope
mounts fall into three main categories, each of which will be
examined.

Equatorial. The equatorial mount, while
being initially difficult to use for a beginner, is the type of mount
prized by the most serious of astronomers. Operating on a dual axis
design, the equatorial mount can, when equipped with a motor drive,
track the stars as they move across the sky during the course of a
night. For this reason alone, it is the choice of the serious
observer and the only choice for any astrophotographer more advanced
than tripod photography. Another plus of the equatorial mount is that
it will come equipped with slow motion controls, which allow for
manual adjustment of the telescope in the most minute motions to
compensate for Earth's rotation without the use of a motor drive. The
only real down side of this mount design is that it can be just about
impossible to point the telescope close to the North Celestial
Pole.Alt-Az.An abbreviation for
“altitude-azimuth,” the alt-az. mount is a simple point and look
affair. For the beginner, this is perhaps the most user-friendly
mount on the market as it is, without doubt, the most intuitive in
use, simply grab, aim, and look. For serious observers who want a
second, often portable mount, a small mount of this design is often
the preferred choice. Like the equatorial, the alt-az can come
equipped with slow motion controls. Unfortunately, unlike on an
equatorial where hand-controlled tracking can be done by turning one
knob if polar alignment is true, no such thing can be done on an
alt-az as you'll find yourself working both knobs simultaneously for
the simple reason that the mount can't align with your latitude.
Also, look out for your tripod legs when aiming.Dobsonian.The
simplest of all telescope mounts, the Dobsonian is essentially an
alt-az using a lazy susan rather than a tripod and mount head design.
First popularized by John Dobson in the 1980s, the Dobsonian has
become the mount choice for large reflectors in recent years thanks
to its simple design, low cost, and the fact that it sits low to the
ground, thus eliminating the need for step stools to get to the
eyepiece. On the down side, the Dobsonian has no slow motion controls
and can be quite a pain to aim when trying to view near zenith.
Still, just by looking how most reflector rigs are sold today will
leave no doubt in one's mind that the Dobsonian is immensely popular.

There
are three main telescope designs, refractor (lens-based), reflector
(mirror-based), and compound (both lenses and mirrors). Each scope
has benefits and drawbacks depending on what you will be observing
and where you will be observing from.

1. Refractors. A refracting
telescope is the oldest telescope design. The first refracting
telescopes were spyglasses intended for terrestrial purposes that
were turned skyward. Galileo’s pioneering discoveries were all made
with a very basic refracting telescope. A refracting telescope uses a
lens to gather the light. The lens is shaped so that the light is
bent (refracted) down to a focus point. After the focus point, the
image is flipped and continues a short distance before hitting a
diagonal mirror which then flips the image back to right side up and
directs it into the eyepiece at the same time. Because of this,
refracting telescopes can also be used for terrestrial pursuits, such
as bird watching. This is the basic anatomy of a refractor. Although
two refractor designs will be dealt with, the difference in the two
types is in the glass used, not the design.

Achromatic refractor. Achromatic
refractors are refracting telescopes with a lens made of two
individual pieces of glass. Commercially made achromatic refractors
usually range from 2 to 6 inches in aperture. The focal ratio usually
ranges from f/5 to f/12. While these are the most common standards,
achromatic refractors can go over 6 inches in aperture or over f/12
in focal length. It is virtually unheard of for a refractor to be
less than an f/5 length. Achromatic refractors provide unrivaled
image sharpness because of a clear aperture and color contrast, which
is created by using a lens. An achromatic refractor will easily out
perform larger scopes of other designs in the area of contrast and
sharpness. While usually marketed for planet and double star
observing, achromats of about 3.5 inches or larger are really
excellent all around telescopes, except in the faint galaxy
department where more aperture is needed. Because of the high color
contrast, refractors are by far the best type of telescope to use in
light polluted settings because the object being observed stands out
well in contrast to the dark background.

There are two major
drawbacks with an achromatic refractor. First, the eyepiece is at the
base of the tube, which means that the eyepiece can be quite low when
observing objects high in the sky. However, the height problem can be
fixed with mount extensions to raise the scope.

The second
problem is chromatic aberration. Because the objective is made of
standard glass, it is difficult to bring light to a single focus
point at focal ratios under about f/12. The colors of the spectrum
have different wavelengths, red having the longest and violet the
shortest wavelength. The goal of the lens is to bring these colors
together at a single point to create an image. However, the glass
used in achromatic refractors can not accomplish this task completely
unless the lens is a long focal length. Because of their shorter
wavelength, colors on the violet end of the spectrum are not brought
to focus with the rest of the colors. The result is a purple halo
around bright objects, especially noticeable at higher powers. Views
of chromatic aberration vary. While some people easily ignore it,
other observers are driven crazy by the false color. Long achromats,
about f/15 or longer, can virtually eliminate chromatic aberration on
all but the brightest objects, but the length can be a problem,
especially for larger aperture scopes.

Apochromatic/ED refractors.
Apochromatic/ED (Extra Low Dispersion) are interchangeable names for
refractors that retain all the high contrast and crystal clear
sharpness of an achromat while eliminating the chromatic aberration.
Without a doubt, apo refractors provide the best images per inch of
aperture of any telescope design. The key to the apo refractor is in
the glass. Apo refractors use anywhere from a two or sometimes even a
five element lens design. With extra layers of high quality ED glass
and strategic spacing in between, an apo refractor can bring all the
colors of the spectrum to a single focus, eliminating any false
color. Apo refractors are usually at least 2.5 inches in aperture and
some companies even offer apos over a foot in diameter. The focal
length is, like the achromat, at least f/5. Large apo refractors are
an astrophotographer’s dream scope. For photography through a
telescope, nothing can beat the combination of pinpoint sharpness,
high contrast, and lack of false color that only an apo refractor can
provide. Like other refractors, an apo can be raised with a mount
extension to bring the scope up to a more reasonable height. With all
of these features going for them, apo refractors are probably the
closest thing to the perfect telescope. However, with apo refractors,
there is a downfall. For all of these perks, any would-be apo owner
will have to pay a premium price. A 3 inch apo optical tube with no
accessories selling for $500 is a bargain. A fully outfitted 4.5 inch
achromat with a tripod and accessories can be bought for about the
same price. But if money is not an object, an apo refractor is
probably the best way to go.

Summary. Refractors, of all the
telescope designs, are the most expensive per inch of aperture. But
if you have the cash, a refractor is well worth the extra investment.
Refractors offer unrivaled image clarity, making them the obvious
choice for anyone who likes to observe planets and/or double stars.
The internal baffling of the tube can greatly reduce internal glare,
boosting the color contrast of your targets. The high color contrast
of a refractor lends itself nicely to light polluted areas. Another
perk of a refractor is the greater light transmission. Refractors
average at least 90% light transmission, with some premium refractors
being tested at as much as 98% light transmission. On the other hand,
the best reflectors only transmit about 75% of the light collected to
your eye. Because of the high contrast and greater light
transmission, a refractor can outperform larger scopes of other
designs for even deep sky objects, especially from cities and
suburbs. Another perk of a refractors are their size, which makes
them easily portable. Achromatic refractors, especially those over 4
inches, are great all around performers and the economical refractor
choice for a beginner. Another big advantage: a closed-tube design,
which means no internal dust, and the fact that it is virtually
impossible to knock a main lens out of alignment without trying.

Reflectors.Physics
pioneer Sir Isaac Newton, bothered by the lack of high quality
refractors on the market at the time, built the first reflecting
telescope around 1668 (exact dates can vary). Reflecting telescopes
use a set of mirrors to gather light. The primary mirror for a
reflector is housed in the rear of the tube. The light enters the
tube, bounces off of the main mirror toward a small secondary mirror,
which then directs the image up through the eyepiece. Unlike
refractors, the image in reflectors stays upside down.

The modern reflector is essentially
unchanged in design from the first one built by Newton and has the
mirror arrangement as described above. Commercially built Newtonian
reflectors can range anywhere from about 4 ½ inches to three feet,
yes three feet, in diameter. The focal ratio of a reflector is
typically an f/4 to f/8 range. Because of their smaller aperture,
small aperture reflectors are typically longer in focal length.
Because of their large diameter, large reflectors are usually at the
short end of the length spectrum. An example of this fact is the
following comparison. A six inch, f/8 reflector is a common design at
about 48 inches long. A ten inch, f/4.5 is another common design,
about 45 inches long. A long focal ratio, large aperture reflector
would just be too difficult to handle. Not many people would want to
mess with a ten inch, f/8 reflector about 80 inches long. The focal
ratio determines what the telescope is best suited for. Long 6 inch,
f/8 reflectors are good all around performers, but are somewhat
limited to a narrow field of view because of the long focal length.
An f/4.5, ten inch reflector is best suited to deep sky observing
because of its large aperture and short focal length, which allows
for a generous field of view. Probably a good, middle of the road
choice is an eight inch, f/6.

Advantages of the reflector include
the mirror light collection system itself. With a mirror, chromatic
aberration is not an issue. Also, a mirror located at the rear of the
tube is less prone to collecting dew than a lens at the front of a
refractor or compound design. The reason many beginners go for
reflectors is the cost. A Newtonian reflector is the cheapest design
per inch of aperture of all telescopes. However, there are drawbacks
to a reflector.

One drawback is due to the mirror system. The
pair of mirrors must be kept in line. Collimating, is the process of
aligning mirrors and this will undoubtedly have to be done sooner or
later. When it comes to handling, Newts are the most fragile of
telescopes. Another drawback of the mirror is that the reflective
coating will need to be replaced with enough time. Bulkiness is an
issue for some people. Many reflectors are typically about four feet
long with apertures of up to a foot. This may prove too large for
some people to want to carry outside very often. For many
astronomers, by far the biggest complaint about Newtonian reflectors
is the secondary mirror. The small secondary mirror is supported by a
four pronged “spider” at the front of the tube. The “legs”
lead to diffraction spikes appearing on stars. While to some people,
the spiking is aesthetically appealing, it is an annoyance to others.
Even for people who think the spiking just adds to the beauty of the
stars, the secondary mirror obstructing the tube definitely degrades
the image sharpness/contrast. Because of the obstruction caused by
the secondary mirror, no reflector will ever match a refractor in the
clarity and resolving department. However, the clarity and resolving
ability of a reflector is not bad at all, it just is not quite as
good as a refractor. Also, while refractors are greatly limited in
size because a lens is only supported on its periphery, a mirror can
be supported underneath, allowing for giant telescopes. Some
companies offer ready built reflectors of up to three feet in
aperture.

Summary. The simple Newtonian
reflector is by far the cheapest telescope design around. Because of
the cost, a six to eight inch reflector is often considered an ideal
choice for a beginning astronomer. Reflectors offer some decided
advantages over other designs. First is the low cost. Reflectors are
also the least likely design to be effected by dew formation. Another
benefit of the mirror is the lack of false color. The older Newtonian
design offers these benefits but has some disadvantages. Mirrors will
occasionally have to be realigned and refinished. Diffraction spikes
provide varying reactions. But the undeniable drawback is the
clarity. While Newtonians can split double stars and resolve detail
in the cloud bands of Jupiter, a refractor will always be better for
clarity and contrast. The new clear aperture reflector design offers
great potential. With the lack of false color and clarity, apo
refractors may soon be challenged as the best telescope design
around.

Compound. The
compound design is a relatively recent idea that uses a system of
mirrors and lenses to produce an image. The light enters the
telescope through either a front plate or corrector lens. From there,
the light travels to the rear of the tube to the primary mirror.
After reflecting off of the primary mirror, the light travels forward
to a small secondary mirror attached either to the corrector lens or
front plate, depending on the design. From the secondary mirror, the
light is directed back toward and through a hole cut in the primary
mirror, finally reaching the eyepiece. Because of the back and forth
reflecting, a compound design telescope tube is much shorter than
either a reflector or refractor, despite being of often longer focal
lengths. The two most common designs here are very similar visually
to a beginner, the differences in the fine details.

Maksutov (Maks) use a spherical,
meniscus shaped corrector lens in the front of the telescope. This
corrector lens is the distinguishing feature of a Maksutov design.
Maks are of often a longer focal ration than the Schmidt design
(mentioned later). The longer focal length results in a less steeply
curved primary mirror, which means less need for image correction.
For the secondary mirror, Maks use an aluminized section on the back
of the corrector lens. This is easier than mounting an actual mirror
but by using the back side of the corrector as a secondary virtually
fixes the focal ratio of a Mak, usually at f/15. Although the field
of view of a Mak is quite small, the small secondary ups the contrast
compared to a Schmidt. Also, because of the use of a glass corrector
lens in the front, Maks are usually limited to about six inches. Any
greater aperture would be too front heavy because of the large lens.

Schmidt. The Schmidt design uses an
aspherical corrector plate as the front objective with a secondary
mirror mounted on the back of the plate. The corrector plate of a
Schmidt is more complex that the corrector lens of a Mak. The Schmidt
corrector plate appears flat, but is actually thicker in the middle
and around the edge. Unlike the Mak, the Schmidt design uses a real
mirror mounted on the back of the corrector plate. Unfortunately, the
secondary obstruction of the Schmidt is the largest percentage of any
telescope design, which degrades image sharpness. The good news about
the Schmidt is that it is shorter, typically f/10, allowing for a
wider field of view than the Mak. Because of this, Schmidts are
better for deep sky viewing. Because of the lighter corrector plate,
Schmidts can be built bigger, up to two feet for commercially built
models.

As with everything else, though, there are
disadvantages. Like Newts, compound designs are obstructed by a
secondary mirror, which will degrade image clarity/sharpness
somewhat. Like refractors, with front-mounted optics, these scopes
are also more prone to dewing up, especially considering that, unlike
refractors, they are often sold without dew shields! AS for the
biggest problem of the compound design it all has to do with the
focusing. Unlike refractors and Newts, which are focused by racking
the focuser in and out, this changing the length of the scope, the
compounds are focused by moving not the eyepiece, but the main
mirror, which creates two problems. First, and most common, mirror
flop. Swinging a compound scope around the sky can actually defocus
the scope because the main mirror will slide around, albeit slightly.
Second, because the tube is not sealed, moisture can actually get
inside the scope, resulting in inner dew and, if the scope in not
allowed to dry, fungus.

Summary. When it comes to portability,
nothing beats a compound design. Models under six inches are an ideal
scope for any astronomer who likes to travel. The great advantages of
the compound design revolves around the short tube design. With the
short tube, looking into the eyepiece will never feel like a
stretching exercise. Large scopes are still compact for their
aperture and are a common choice for anyone considering building an
observatory with a permanently mounted telescope. Like the reflector,
chromatic aberration is never an issue. Maksutovs have small fields
of view but provide clearer, higher contrast images because of the
smaller secondary mirror. Schmidts are shorter and can be built
bigger, but at the price of having a substantially larger secondary
mirror than the Mak. Either way, size wise, nothing beats a compound
design.

What is best? The question of what
is the best telescope has no right or wrong answer. What constitutes
an ideal scope is determined by where the scope will be used and the
preferences of the observer. In only a few situations can any actual
recommendation be given with confidence. If you live in a light
polluted city where only planets and bright stars are visible, a
small refractor is the way to go, unless you know of a dark site you
can go to in the country. Even a 60mm refractor at high power can be
used to successfully reveal the cloud bands of Jupiter, the rings of
Saturn, and split many double stars. From a bright city setting,
trying to find deep sky objects will be a futile search, making a
large aperture, deep sky scope useless for its intended purpose. For
observers living under dark skies where the Milky Way is easily
visible, aperture should be the goal. Because deep sky objects will
be easily seen, the largest telescope that can be easily taken
outside would be the ideal scope. Just be careful not to go too big.
A scope too big to transport easily will probably hardly ever get
used. A small compound, under 6 inches, is ideal for anyone who likes
to take their hobby out on the road. Some small scopes can be made to
fit a lightweight camera tripod, which are perfect for traveling
astronomers. For anywhere in between, and recommendations are hard to
give. A great piece of advice for someone buying a telescope is to go
to a star party and look through as many types of telescopes as
possible. The best way to discover your personal preferences is to
look, reading descriptions can only go so far. According to many
astronomers, the best telescope is one that will be used and not left
to sit and collect dust in a closet.

Spotting scopes, intended for nature
watching, are also great for beginners when turned skyward. Spotting
scopes are small telescopes of either refractor or compound design.
The reason that you will never see a reflecting spotting scope is
that reflectors always produce upside down images.

While spotting scopes are more
expensive than binoculars, they do offer some advantages. Some
spotting scopes come with a tripod and even if it doesn’t come with
a tripod, all spotting scopes can be made to attach to tripods to
provide a stable viewing platform. Another great benefit of spotting
scopes is that many have adjustable magnifications that usually range
from 20x up to 60x. The adjustable magnification is great for finding
objects and then zooming in on them. The only downfall is that even
at low power, 20x, the field of view will be quite small. At 60x, you
have the equivalent of low power for an astronomical telescope. Some
spotting scopes even come with eyepieces like an astronomical
telescope. Some spotting scope eyepieces can also be used on an
astronomical telescope when you decide to upgrade.

As with binoculars, spotting scopes
can have their viewing field expressed in degrees or feet at a
particular distance. Use the same method as for binoculars to
calculate the field if it is expressed in feet. Again, higher
magnification reduces the field of view.

Like binoculars, aperture is
important. The larger the aperture, the better.

Binoculars
are essentially two small refracting telescopes put together and are
very cheap, but can be great for looking at the stars, especially
when coupled with a tripod to eliminate the shaking that we all have
some degree of in our hands. With the shaking eliminated, dimmer
objects can be resolved.

When it comes to buying binoculars,
they can be picked up at most department and sporting goods stores
for under $50. For beginners, any binoculars will do, as long as they
met a few basic specifications that are suited to astronomy.

Binoculars are sized by two numbers,
10x50, for example. The 10 refers to the magnification power and the
50 refers to the lens aperture. For astronomy, a pair of binoculars
with a magnification of ten or twelve is ideal. Anything less that
ten is often underpowered for viewing some brighter deep sky objects,
especially if light pollution is an issue. Anything much greater than
twelve often is a problem because of two factors. First, at higher
magnifications, shaking in your hands can really become a problem.
Second, the higher the power, the smaller the field of view. Even for
experienced astronomers, a generous field of view is desired to
eliminate any need to search, which is better spent looking at the
sky. With binoculars, searching should not consume much time.

The second number, the aperture, is
also important. Anything less than 50mm won’t let enough light in,
which will limit what you can see. In astronomy, aperture is
everything. For aperture, higher is always better. If you find two
pairs of binoculars for close to the same price, say a 10x50 and a
10x70, go for the one with the larger aperture. With a larger lens,
more light is let in and objects will look brighter.

Another important consideration for
astronomy binoculars is field of view. For most people, anything less
than a 5 degree field will be too small thanks to both the narrow
field making things harder to find and for being more prone to hand
shake. Personally, anything with a 5-7 degree field is the happy
medium. Generally speaking, binoculars with 7-10x power fall into
these fields of view.

Sunday, November 3, 2013

Like the Sun, the stars move in the
night sky. For proof of this, go out on any clear night and look up,
noting the positions of a few bright stars, then go back inside for a
few hours. Later in the night, go out again and, guess what, the
stars have shifted position.

So, how does this work?The most
important thing to understand is that the sky itself does not move,
the Earth moves and the motion of the sky is only apparent. So in
technical terms, referring to “sunrise” or “sunset” is
incorrect as the Sun doesn't move. The motion of the Sun, and other
stars, is caused by the rotation of the Earth. The Sun and Stars are
all at fixed points in space and the Earth is not. For an easy
comparison, stand in a room and twirl around. By doing this, you are
simulating the relationship of Earth to the stars. You are the
rotating Earth and everything in the room is a star. Objects in the
room appear to move even though you know they are stationary, only
you are actually moving. The situation is the same for the Earth and
stars. Ironically, despite knowing this fact for hundreds of years,
we still have yet to adopt it into our daily language.

If you go outside and observe the
location of the Northern stars over the course of a night, you will
notice that they revolve around a single point in the sky. The
question quickly becomes “why?” The answer is simple. The Earth
is surrounded by stars in all directions. Imagining a giant arrow
starting at the Earth's South Pole, extending through the core of the
planet, to the North Pole, and out into space. The North
Celestial Pole lies directly overhead of the Earth where the
head of the arrow is pointing. In a modification of the experiment in
the above paragraph, twirl yourself around in a room looking straight
up at a fixed point on the ceiling. The point you are looking at will
remain stationary and everything else you see will seem to revolve
around that fixed point. The same exact thing happens with the Earth.
In fact, every star revolves around the Celestial Pole, but those
stars that are far enough away from the pole, out of the circumpolar
region of sky, appear to rise in the East and set in the West. Over
the South Celestial Pole, the same thing happens as in the North.

The rarest of all celestial visitors
visible to the naked eye, comets are capable of, by far, the most
variety. When one hears the word 'comet,' the thought of a
long-tailed object comes to mind. Yes, while comets can look like
this, these 'great comets;' are exceedingly rare. To illustrate, the
last great comet, McNaught, was visible in 2006-7. Before that,
Hale-Bopp (1997) was the last great comet. While there was Hyakutake
the year before in 1996, Halley's Comet's 1986 appearance was the
last great comet before that. Just by looking at these examples, the
pattern becomes obvious: great comets are, on average, a once a
decade event.

Now, while not all comets are the pop
culture image great comets present, they are fun to look at. With the
naked eye, comets can be visible as diffuse fuzzball-like objects in
the sky. In binoculars and telescopes, comets can take on a lot more
detail, especially in regards to color. For comets, the most common
color is a greenish blue, which can be extremely delightful to look
at in the telescope as there are no green objects in the sky.

Another interesting point to comets is
that they are unpredictable. While forecasters will make predictions
about what any given comet will do months in advance of its arrival,
comets often have other ideas. A prime example of this was Comet
Holmes in 2007, which morphed from a small, normal
binocular/telescopic comet just on the edge of naked eye visibility
into a massive body as large as the full Moon. The same can be said
of Comet McNaught. While bright, no one could have ever expected it
to erupt a sky-spanning tail after making its close passage to the
Sun. To say the least, comets are true cosmic wild cards that are
always worth a look.

Of
all heavenly bodies, the Moon is perhaps the most fun to observe with
the naked eye thanks to the fact that it changes phases and because
one can actually see surface features without optical aid.

When
it comes to Moon's phases, they are actually very easy to explain.
Although it may not always appear so to us, the Moon is always half
lit. What we can see and when we can see it depends on where the Moon
is in its orbit relative to the observer. To explain what is
happening, let’s take a trip around the Earth by way of the Moon. A
total orbit of the Moon around the Earth takes about 29 days. At new
Moon, the alignment is Sun, Moon, and Earth in that order and in a
straight line. From the Earth, the Moon is lost in the glare of the
Sun, hence why we cannot see it. As the days progress, the Moon will
move out of the Sun’s glare and the Sun will set before the Moon.
In the days just after new Moon, from the Earth, we will begin to see
a tiny bit of the lit side of the Moon just after sunset.

As
the days progress, we will continue to see more of the lit side of
the Moon as our cosmic companion distances itself from the Sun’s
glare. As the Moon moves from new to first quarter, it
is called a waxing crescent. At first quarter, the point in
its orbit where the Moon has gone a quarter of the way around the
Earth, the Sun, Earth, and Moon form a 90 degree angle, with Earth
serving as the right angle of an imaginary cosmic triangle. Because
of this 90 degree angle, the Moon appears half lit to us on Earth
because we see exactly half of its lit side. At first quarter, the
Moon also rises exactly half way between sunrise and sunset.

As
the moon continues in its orbit from First Quarter, it is now farther
from the Sun than the Earth. After the angle to the Moon relative to
the Earth is over 90 degrees, we see more than half of the lit side
of the Moon and the Moon continues to rise later each night. At this
point of being over half full, the Moon is now called a waxing
gibbous.

At
full
Moon,
the Sun, Earth, and Moon are all in a straight line relative to each
other. The Moon is now appears full as we can see the entire lit side
because it is directly opposite the Sun in the sky. After full Moon,
the Moon continues its orbit, now traveling back toward the sun as a
waning
gibbous. We see less and less of the lit side of the Moon as it
returns toward the Sun. At third quarter, when the Moon reaches a 270
degree angle from the Sun, we again see half of the lit side and half
of the dark side. The Moon now rises exactly between sunset and
sunrise. After third quarter, the Moon now moves even closer to the
Sun as a waning crescent, rising later each day until it is again
lost in the glare of the Sun as a new Moon.

First of all, this should go without saying, but
NEVER look at the Sun without specialized eye protection, whether it
be in the form of eclipse glasses or solar filters for
binoculars/telescopes. For penny pinchers who do not want to use
eclipse shades, a #14 or darker welder's shield will work when
observing the Sun with the eye alone. When looking at the Sun with
the naked eye, it will often appear as a single-colored disk save a
few large, dark sunspots. When turning binoculars and even or
powerful telescopes on the Sun, the spots will appear more detailed,
with clear shapes becoming visible.In telescopes, the real fun
starts when moving out of visible light into very specific
wavelengths. By doing this, one will be able to see granulation,
which gives the Sun the appearance of boiling water, flares, which
appear as giant flames erupting off the solar surface, and prominences, arches of fire that loop up and then down again.
Unfortunately, all of this added detail comes at a cost, literally,
as such filters/specially-built telescopes cost a lot more than
standard, visible light filters.

Only
five planets, Mercury, Venus, Mars, Jupiter, and Saturn are visible
to the naked eye. Under extremely dark skies, Uranus can be spotted
but is indistinguishable from the stellar background and Neptune
requires binoculars to even be seen at all. Many ways exist for
classifying the planets. For observational purposes, only one
classification really matters. For observers, the two types of
planets are inferior planets within the Earth’s orbit and
superior planets outside the Earth’s orbit. Where a planet
is in relation to the Earth directly impacts its apparent motion
throughout the sky. However, irregardless of where a planet is in
relation to Earth's orbit, they all lie on the ecliptic plane,
a narrow lane of sky wherein planets appear to travel and that
represents the area where a disc of dust and debris existed at the
formation of the solar system. In time and with the aid of gravity,
this debris coalesced to form the planets. Inferior Planets

Inferior
planets are never seen to stray far from the solar glare and are only
visible in the morning or evening. For planets within the Earth’s
orbit, knowing some terminology is necessary. Greatest elongation,
Eastern or Western, is the best time for observing the inferior
planets. Greatest elongation refers to the time in a planet’s orbit
where the planet is at its greatest angular distance from the Sun and
at its highest in the sky as seen from Earth. Eastern elongation is
when the planet is farthest East of the sun and this means the planet
is visible in the evening and Western elongation means the planet is
visible in the morning when it is farthest West of the sun. The worst
time for observing an inferior Earth planet is during conjunction.
For planets within the Earth’s orbit, there are superior and
inferior conjunctions. A superior conjunction is when the
planet being observed is on the far side of the Sun in a straight
planet, Sun, Earth alignment. Inferior conjunctions occur when the
planet comes between the Earth and Sun in a straight Sun, planet,
Earth alignment. Either way, any conjunction is the time when a
planet disappears into the sun’s glare.

Mercury.
Of all the planets, Mercury is the one most people never see.
The great astronomer Nicholas Copernicus, who finally rediscovered
the idea that the sun is the center of the solar system, reportedly
never saw Mercury. The reason that Mercury is so difficult to spot is
that it is so close to the Sun. The greatest possible elongation only
takes Mercury about 28 degrees away from the sun. Because the
ecliptic is rarely vertical, Mercury at greatest elongation actually
appears much lower that 28 degrees in the sky most of the time.
Because Mercury is an inferior planet, it is only seen in the early
morning just before sunrise and early evening just after sunset.
Mercury is best seen in spring evenings and on fall mornings when the
ecliptic is nearly vertical, allowing Mercury to appear highest in
the sky. When seen, Mercury averages out to be about a zero magnitude
object near the horizon. Even though it is bright, because it is so
close to the Sun, Mercury is often difficult to spot. Binoculars cure
this problem. Because the sky needs to dim before the planet can be
seen, any time that Mercury appears about ten degrees above the
horizon is considered a good appearance. If you see Mercury, you will
join an exclusive club of people who have seen the planet nearest to
the Sun.

When looking an Mercury with binoculars, it still
looks like a bright star without any special features.

In the
higher power of telescopes, Mercury appears to go through a complete
set of phases from new to full and back again, just like the Moon.
While interesting to watch in the present, in the past, the phases of
Mercury (and Venus) conformed the theory that the planets do go
around the Sun, not vice versa.

Venus As the third brightest object in the solar system, only
out-shown by the Sun and Moon, Venus is a true sight to behold. Venus
is the second planet from the Sun and, because it lies within Earth's
orbit, is classified as inferior. Because of its location relative to
Earth, Venus can only be seen in the morning or evening. Averaging
out at about magnitude -4, Venus cannot be missed. The greatest
elongation possible for Venus is about 47 degrees. The best times for
viewing Venus are Spring evenings and Fall mornings, when Venus can
be seen about half way up to the zenith during a good appearance. At
other times of year when the ecliptic is at a flatter angle, Venus
appears much closer to the horizon. Because of its brightness and
movement in relation to the Sun, Venus was given special significance
by many ancient cultures, especially the Maya of Central America, who
considered Venus just as important as the Sun. Because of its
brightness, Venus is very easy to spot. So go outside when Venus is
at its best placement, you can’t miss it.

When looking at
Venus through binoculars, it may be possible to see phases if the
binoculars are strong enough (above 15x power) and are mounted on a
tripod.

In telescopes, Venus can appear to be a mini Moon because
of its very obvious phases. Because it is closer to us then Mercury,
when watching the phases of Venus, look for changes in the planet's
angular size as the planet will appear at its largest as a crescent
and its smallest as it nears full.

Superior
Planets

Planets
outside the Earth’s orbit exhibit different patterns of behavior.
Depending on the location of the planet in its orbit, planets outside
the Earth’s orbit can be observed at any time of the night and can
be seen to traverse the sky, rising and setting with the stars. Here,
a new term, opposition, enters the equation. Opposition is the
time when a planet is 180 degrees away, directly opposite the Sun in
the sky. This means that when a planet is at opposition, the planet
rises as the Sun sets and sets as the Sun rises. At and around
opposition, a planet is observable just about all night. Looking down
on the solar system from above, opposition is a straight line of Sun,
Earth, and planet. For outer planets, there is only one type of
conjunction when the planet goes behind the Sun in relation to Earth,
the superior conjunction of an inferior planet. And like the inner
planets, outer planets are un-observable at and near conjunction.
Another interesting phenomena takes place with the superior planets
is retrograde motion, which is caused when the Earth passes a
slower planet. A similar comparison is when you are driving on a
highway and pass a slower car, which appears to fall behind you
because it is being passed by your faster-moving car. A third bonus
of the superior planets is that, along the ecliptic, lie some
magnificent star clusters which the planets can appear to pass near
or actually through.

MarsOf all the planets, Mars is
often considered the most fun to visually observe. Because it is a
superior planet, Mars retrogrades. But the real bonus with Mars comes
about because of its highly elliptical orbit. While all planets
change in brightness, most do only slightly. Mars is the notable
exception. At its dimmest, Mars shines just shy of +2 magnitude. At
its brightest, an obviously red Mars nearly reaches magnitude -3.
Because of the highly elliptical orbit, the distance from Mars to
Earth changes more than any other planet. The changes in
distance bring about the dramatic changes in brightness. Mars is also
notable because detail of the planet, its red color, can be observed
without a telescope. Of all the planets, Mars is the probably the
most fun planet to observe today while it was probably the biggest
anomaly for ancient astronomers to explain. By observing Mars over
the course of its 2-year orbit and various changes, it's no wonder
that the ancients thought that it was alive.

In binoculars, Mars does not appear
any different than it does to the naked eye, just a bigger, and more
red. In telescopes, though, Mars can be a real treat. By using a
medium-sized (4” and up) scope at around 200x power or greater,
surface detail of Mars can become apparent, especially when Mars
makes a close approach to Earth. The first things to look for on Mars
are its polar ice caps, not unlike those of Earth, which can actually
build and recede according to the Martian seasons. If you have a
really big scope and really steady skies, more can be seen on the
Martian surface, namely Mariner Valley, a canyon that would stretch
from New York to Los Angeles if transported to Earth. Under the best
conditions, one can observe differing colors on the Martian surface,
which can, from time to time, be obscured my massive sand storms,
whose existence is evidenced by temporary changes to the Martian
surface coloring. In years past, it was thought that such changes in
surface color were caused by the blooming and dying of of vegetation,
much like that of deciduous trees here on Earth

JupiterJupiter is the largest
planet in the solar system and, because of its great distance, shines
at a relatively constant -2.5 magnitude. Because of its twelve year
orbit, Jupiter takes spends about a year in each zodiac
constellation before moving on to the next. To the naked eye,
Jupiter appears only as a bright star.With optical aid, the game
changes dramatically. In binoculars, while the cloud bands will still
be invisible, one should be able to see the 'Galilean Moons,' named
after their discoverer, the Italian astronomer Galileo. These four
largest moons of Jupiter are named Io, Europa, Ganymede, and Callisto
and are in that same order, with Io being closest to Jupiter and
Callisto farthest. A simple way to remember them is to say 'I(Io)
Eat(Europa) Green(Ganymede) Caterpillars(Callisto).' Okay, it's a
little juvenile, but it works. For historical implications, the
discovery of Jupiter's moons proved that not all objects went around
the Sun, which was preached as gospel by science and Church until
that time. Also, in binoculars, Jupiter transforms from looking like
a bright star into a very obvious planetary disc. To see this, just
look at the edges of the planet, which appear as a crisp line and not
a diffuse glow. In telescopes, Jupiter transforms from a
featureless disc into a world alive with color. In even small
telescopes, one can see distinct, reddish-pink cloud bands on the
planet. The higher the power, the more detail one can resolve. In
large scopes under steady skies, expect to see, with relative ease,
swirling in the clouds along with the Great Red Spot. Another cool
feature to be seen in a telescope at high power is the shadows of the
Galilean Moons transiting the disc of the planet itself. Though not
overly rare, these are fun events to observe, especially for a
beginning astronomer.

SaturnThe last planet known to
the ancients and the second largest planet, Saturn appears to the
naked eye as a star shining around magnitude -.5. Saturn takes about
30 years to orbit the Sun and thus spends just over two years in any
given constellation of the zodiac. Like Jupiter, Saturn shines at a
relatively constant brightness thanks to its immense distance from
Earth.In high-powered binoculars on a tripod, Saturn's famous
rings, while not being truly resolved, do present themselves in that
the planet seems to have an oval shape to it, which Galileo termed as
“ears.”.Like Jupiter, even the smallest telescopes
transform Saturn from a featureless disc into a wonderful world that
must be seen to be believed. First of all, there are the famous
rings, which appear easily at around 50x power. With larger scopes
and higher powers, one can see gaps in the rings, most famously the
Cassini Division. With very large scopes under steady skies, smaller
divisions may also appear on a good night. Another thing to look for
with Saturn are color bands, which are far more subtle than on
Jupiter. With Saturn's rings, there is an interesting phenomenon that
takes years to present itself. Because of the angles of Earth and
Saturn relative to each other, Saturn's rings appear to 'open' and
'close,' with, once every 15 years years, the rings becoming edge-on and
disappearing from view altogether. This slow progression can be
observed in even the smallest of telescopes. Back to the big scopes,
look for Saturn's moons. While giant Titan is easy to see, it can be
possible to spot some of the other, much smaller ones, too.

Even
before going out and taking your first serious look at the night sky,
you undoubtedly know that some stars are brighter than others. In
astronomical jargon, the brightness of a star is known as magnitude.
The magnitude scale is unusual in that it works in both positive and
negative numbers. On the scale of brightness, the lower the number,
the brighter the object.

There
are two kinds of magnitudes, apparent and absolute. The absolute
magnitude is the actual brightness of a star. Stellar distances
greatly vary. Some small stars that give off a relatively small
amount of light are close and appear bright while some giant stars
are very far away but appear dim. A comparison can be made with light
bulbs. A nightlight at five feet away will look brighter than a 100
watt bulb at 300 feet away. The same is true of the stars. But for
observational purposes, the magnitude to be concerned is the apparent
magnitude, which simply refers to how bright the star appears to
be in the night sky. The Sun, undoubtedly the brightest object in
the sky, blazes away at an apparent magnitude of -27 while, for most
people, a magnitude of +5 to +6 is the naked eye limit on the dim
side of the spectrum. Needless to say, a combination of good eyes and
dark sky can produce the ability to see even dimmer stars.

The
magnitude scale is not an arithmatic scale because stellar brightness
does not increase or decrease by a factor of one. A difference of one
stellar magnitude translates to about a 2.5 change in brightness. For
example, a zero magnitude star is about 2.5 times brighter than a
first magnitude star. To compare brightness of stars, just multiply
2.5 to the power of magnitude difference. For example, to find the
magnitude difference between a third and zero magnitude star,
multiply 2.5 x 2.5 x 2.5 (2.5 to the third power) for an answer of
15.6, which means that the zero magnitude star is about 16 times
brighter than the third magnitude star.

After
brightness, the next thing to look at with stars is their color,
which is a direct giveaway to a star's temperature. When it comes to
stellar classifications by color/temperature, there are 7 classes
that matter to the visual astronomer: O, B, A, F, G, K, M. A common
way to remember this is by the saying 'Oh(O), be(B) a(A) fine(F)
girl/guy(G), kiss(K) me(M)!' For students, the saying 'Oh boy, an 'F'
grade kills me!' will also work equally well. When it comes to what
the classifications mean, here's what we get:

Generally speaking, most of
the stars in the sky fall between the A and G classification. Want
proof of this? Just go out and look up. Now, it should be said that
the stars do not look like Christmas lights in the sky, the colors
are far more subtle. Still, though, by looking around the night sky,
one can see that, while not obvious, the stellar colors mentioned
above are, without doubt, very present. Obviously, in a telescope,
the colors become very apparent.

Like the Sun, the stars move in the
night sky. For proof of this, go out on any clear night and look up,
noting the positions of a few bright stars, then go back inside for a
few hours. Later in the night, go out again and, guess what, the
stars have shifted position.

So, how does this work? The most
important thing to understand is that the sky itself does not move,
the Earth moves and the motion of the sky is only apparent. So in
technical terms, referring to “sunrise” or “sunset” is
incorrect as the Sun doesn't move. The motion of the Sun, and other
stars, is caused by the rotation of the Earth. The Sun and Stars are
all at fixed points in space and the Earth is not. For an easy
comparison, stand in a room and twirl around. By doing this, you are
simulating the relationship of Earth to the stars. You are the
rotating Earth and everything in the room is a star. Objects in the
room appear to move even though you know they are stationary, only
you are actually moving. The situation is the same for the Earth and
stars. Ironically, despite knowing this fact for hundreds of years,
we still have yet to adopt it into our daily language.

If you go outside and observe the
location of the Northern stars over the course of a night, you will
notice that they revolve around a single point in the sky. The
question quickly becomes “why?” The answer is simple. The Earth
is surrounded by stars in all directions. Imagining a giant arrow
starting at the Earth's South Pole, extending through the core of the
planet, to the North Pole, and out into space. The North
Celestial Pole lies directly overhead of the Earth where the
head of the arrow is pointing. In a modification of the experiment in
the above paragraph, twirl yourself around in a room looking straight
up at a fixed point on the ceiling. The point you are looking at will
remain stationary and everything else you see will seem to revolve
around that fixed point. The same exact thing happens with the Earth.
In fact, every star revolves around the Celestial Pole, but those
stars that are far enough away from the pole, out of the circumpolar
region of sky, appear to rise in the East and set in the West. Over
the South Celestial Pole, the same thing happens as in the North.